The other of the 2 Reclining-Declining formulas listed in the notes, at the bottom of the wikipedia Sundial article, likewise gives correct answers.
Again, using: Lat = 51.5 Incline = 45 Decline direction = 45 degrees left of south ...The Mayall & Mayall formula, in the article's notes, for Hrd--gives the correct answer for the angle between the 8:00 a.m. line and the noon line on the dial. If the line for a particular hour is counterclockwise from the noon line, then that answer is given as negative, (or maybe under some circumstances, as the positive number consisting ofthe sum of that negative + 360). Let me repeat some things about the use of those formulas: Where Hrd1 and Hrd2 appear at the left side of the two equations, Hrd1 should be replaced by tan Hrd1, and Hrd2 should be replaced by tan Hrd2. The equation Hrd = Hrd1 + Hrd2 is correct as shown. D, the decline direction, is measured from north. It's the azimuth that the dial is facing. R, the recline, is measured from the horizontal. (Nowadays that's probably more often called "incline" and represented by "I"). So, both of the Mayall & Mayall Reclining-Declining formulas in the notes at the bottom of the wikipedia Sundial article are correct, and give the correct answer. MichaelOssipoff
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